Without water no animal can survive. In desert regions, especially, the greatest threat to life is desiccation—or, quite simply, drying up. But many creatures have achieved specialized adaptations to make full use of what little water exists in arid areas.
One of nature's masterpieces among creatures equipped to cope with desert life is the hardy camel. When H. St. John B. Philby made his historic crossing of The Empty Quarter in 1932, a Texas-sized desert in Saudi Arabia, his camels had no water for ten days of the final march of 375 miles, other than emergency rations for such animals as were in danger of collapse. Only an occasional "snuffing" was permitted. This, as Philby explains, was "an economical method of refreshing camels by administering a kettleful of water through the nostrils to cool the head and brain."
Stories range the desert lands far and wide about remarkable endurance feats by camels. It is said that one of the more famous records was set by Shaikh Naif ibn Humaid of the 'Utaiba tribe who rode from Riyadh on an urgent mission in the middle twenties and covered close to 800 miles in eight days.
The popular belief that camels store water in their humps is correct in substance: water is indeed stored there but in the form of fat. On long, waterless marches the camel draws on this reserve (as well as on the water stored in three special reservoir compartments in its stomach) by making metabolic water.
Anyone who has seen fat spluttering in a pan has seen the process: the spluttering is caused by water escaping from the fat in the form of steam bubbles. Something of the same sort occurs inside the body of the camel and other desert creatures. Water is released by the breaking down of sugars and other carbohydrates or by the oxidation of the hydrogen or carbon.
The camel, too, has a very special kind of blood. A camel loses very little fluid from its blood stream when it does not drink for days at a time. In contrast, the blood of most animals, including man, becomes so thick that finally the heart can't pump it through the system.
The deserts of the world are indeed populated but only by creatures having ingenious adaptations. American oil men exploring the vast Rub' al-Khali regularly run across the tracks of desert creatures. When St. John Philby crossed this huge arid area three decades ago, he gathered many specimens, such as the desert fox, cat, hare, jerboa, the oryx and white gazelle. He collected 14 species of birds, a dozen reptiles and many insects.
Some animals such as the Arabian or white oryx and its near relative, the addax, the gazelle, the jerboa and the desert mouse get sufficient water from dew and their food. In the strict sense of the word, they are non-water drinkers. Others such as the ostrich, giraffe, eland and pocket gopher also get much of their water from their food.
Many desert plants are good water sources for creatures with the right kind of stomach or mouth. The camel's leathery lips enable it to eat spiky plants that most other animals would not be able to swallow but which contain as much as 80 per cent water. The camel can even dine happily on razor-spined prickly pear found in North Africa.
Some desert reptiles get much of their water from dining on insects such as ants and locusts, which have a very high water content. Tiny lizards, only three or four inches long, may eat 600 to 700 ants during a single day. Both the waral (snake-headed monitor) and the dhub (spine-tailed monitor) of Arabia get much of their water from insects, and particularly from grasshoppers and locusts. The waral has yet another water source in the snakes on which it preys.
Arabian desert carnivores such as the fox, cat, wolf, cheetah, jackal and the panther also get much of their water from freshly-killed prey. Most carnivores, indeed, do so-even the desert cat can live for weeks with no moisture intake other than water contained in newly slain food.
Many desert reptiles store food and water in deposits of fat in their bodies and tails. It has been reported that a species of Gecko lizard, in a laboratory experiment, lived for a year without food or water.
Another piece of nice adaptability designed by nature is the almost impervious body coverings of some of the more successful dwellers of desert and arid regions. These include reptiles (the most numerous), birds, many insects and some specialized animals. Some mammals such as men, apes and horses lose much water (and salt) through sweat glands. But most rodents and some ruminants—certain antelopes, for instance—nearly or completely lack sweat glands.
But even non-sweating creatures need other talents if they are to flourish in arid regions. Many desert creatures are nocturnal and thus conserve moisture. They avoid the desiccating effects of high day temperatures and low humidity. The deserts are never so populous as they are at night—as a silent observer can hear and see.
Reptiles active during the day have particular problems. Day temperatures may go as high as 120 degrees F. and ground temperatures may go over 140 degrees F.—15 to 35 degrees above the lethal temperature for a day-active lizard. How, then, do so-called "cold-blooded" animals maintain their body temperatures some 20 degrees below their surroundings? They do so in a number of ways. Some raise their bodies and tails from the ground to leave an insulating layer of air between their bodies and the hot sand. Diurnal desert lizards almost invariably have an immaculate white belly which reflects heat from the hot ground. When they get too hot, some lizards pant, causing a respiratory heat loss that reduces body temperatures.
Burrowing is another reptilian way of coping with excessive temperatures. Both Old and New World lizards often have broad bodies designed for burrowing into loose soil or sand by lateral and vertical movements. Indeed, the remarkable spiral technique of the sidewinder of the Southwestern United States is also used by small horned vipers in North Africa and Arabia. And valve-like closing of nostrils, eyes and mouth in lizards and snakes burrowing in loose sand is found both in Arabia and California. On the other hand, the giant land lizards (chuck-wallas) of the arid Gulf of California survive the easy way—they have learned to drink salt water!
Many desert creatures are migrants and nomads, moving on when food and water become scarce. But desert snails aren't able to do so, and they have acquired the ability to put themselves into "cold-storage"—or, more correctly, into "nearly-desiccated" storage. Two specimens of the desert snail Helix desertorum were glued to cardboard and exhibited in the British Museum in 1846. Four years later an entomologist wondered what would happen if the dried-out creatures were placed in water. One actually revived!
Some desert animals emulate the snails, though not quite so dramatically. During hot summers and periods of drought they estivate—the word means "to pass the summer." Many reptiles estivate. Among the more accomplished are some water-storing frogs of the more arid regions of Australia and North America. The reservoir frog lives and breeds in pools which fill up in the rainy season. When the sun empties the pools, the frog goes down several feet into the mud, and after distending itself with water, shapes out a little moist cell whose walls later become dry, hard, and insulating. There the frog, in a torpor that is profound though not as deep as that of hibernation, calmly sits it out until the next rainy season.
The most remarkable of animal estivators are probably the desert ground squirrels, such as those found in the Turkestan deserts and elsewhere. These squirrels are active only for three and a half or four months each year, during the period when there is green vegetation. Their summer estivation merges almost directly into a winter hibernation.
Life in deserts is strenuous and difficult. Death from desiccation and also starvation threatens constantly. A British climber on one of the Everest expeditions reported that on some of the arid Tibetan uplands the tufts of herbage were so few and far between the mountain sheep could only get enough to survive by running between mouthfuls. They chased their grass!